This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Due to increasing life expectancy, women can expect to live one-third of their lives after menopause. The loss of estrogen and progesterone is the most dramatic physiological change that occurs in aged women. Aging is also accompanied by a decline in immunity that contributes significantly to morbidity and mortality in older individuals. The impact of menopause on immune senescence remains poorly understood. We proposed to test the hypothesis that loss of ovarian steroids exacerbates immune senescence and that estrogen replacement therapy can restore T cell function in female rhesus macaques.